1. Field of the Invention
The present invention relates to a three-phase gas insulated bus and more particularly to an improvement in an insulating spacer for supporting three three-phase conductors inside a grounded metal sheath.
2. Description of the Prior Art
A conventional gas insulated bus in general includes a grounded cylindrical metal sheath, high voltage conductors arranged inside the sheath, an insulating spacer for supporting the conductors apart from the sheath, and an insulating gas such as sulfur hexafluoride (SF6) sealed within the sheath.
In case it is not desired to gas-tightly separate portions of the grounded metal sheath by the insulating spacer, a pillar-shaped insulating spacer or an integrally molded insulating spacer has mainly been used.
The pillar-shaped insulating spacer is mounted on the inner wall of the sheath and individually supports each of the three three-phase conductors. The integrally molded insulating spacer integrally insulatingly supports three high voltage conductors and is fixed on the inner wall of the sheath at a plurality of extending portions of the spacer.
However, the grounded cylindrical metal sheath is not exactly circular in shape when the sheath is manufactured. Since the manufactured sheath becomes approximately circular in shape when high pressure insulating gas is introduced into the sheath, the configuration of the sheath varies before and after gas filling.
In the pillar-shaped insulating spacer, hardly any stress is applied to the spacer, even if the cylindrical metal sheath is deformed. The distances between each of the conductors shift as the sheath is deformed.
On the other hand, in the integrally molded insulating spacer, the supporting parts of the spacer are firmly fixed on the inner wall of the sheath. As a result, large stresses are generated in the spacer by deformation of the sheath during gas-filling, and the spacer is destroyed or suffers from shortening of its life.